This invention concerns a method to evaluate the quality of grapes.
The invention also concerns the device suitable to achieve the method.
The invention is applied mostly, but not exclusively, in the field of wine-making, to perform a rigorous and selective evaluation of the quality of a sample of grape juice in order to discriminate the quality level of the grapes from which the juice has been obtained, and to allow it to be classified according to its actual polyphenol composition and characteristics.
In the state of the art, and in the field of evaluating the quality of grape juice obtained from a particular batch of grapes, and/or of the grapes themselves from which the juice comes, the most commonly used procedure at present provides to analyse the sugar content of the sample.
This procedure is sometimes integrated, or more rarely replaced, by an analysis of the titratable acidity of the sample, in order to obtain further information and to allow to classify the sample more reliably and more rigorously into a certain class of commodity.
However, analysing the titratable acidity requires equipment which is not always available and times which are sometimes not compatible with the requirements of the producing companies.
Moreover, the factors which determine the quality of the grapes, and in general of fruit and vegetable juices, are not limited only to the presence and percentage of sugars and/or acids dissolved in the juice; they are also linked to the presence of particular substances, mainly such as polyphenolic substances and aromatic substances.
At present, however, the percentage of these substances in the grapes is never quantified when the technological procedures to transform the grapes into wine are begun.
Therefore, the commodity classification of the various qualities of grapes is not rigorous and does not give an efficient, selective and objective discrimination into a plurality of quality levels according to the actual composition characteristics of the juices obtained from the various batches of grapes.
Various solutions have been proposed in the state of the art which exploit a colorimetric analysis of a juice, usually carried out with sources of light operating in the region of infra-red, in order to determine some characteristics thereof.
For example, the article xe2x80x9cContinuous Colorimetryxe2x80x9d by F. M. Clydesdale, taken from the journal xe2x80x9cInstrumentation in the Food and Beverage Industryxe2x80x9d, vol. 2, 1973, pages 33-43, describes a method of spectrophotometric analysis made on a plurality of samples of blueberry juice in order to verify the content of colored pigments in said samples.
The purpose of the analysis is to select, in an analytical manner, samples of juice which answer desired visual criteria of color.
This document does not teach to construct quality classes of the product from which the juice is obtained according to calorimetric analyses.
The article xe2x80x9cApplication for Near Infrared Spectroscopy for Predicting the Sugar Content of Fruit Juicesxe2x80x9d, taken from the Journal of Food Science, vol. 49, 1984, pages 995-998 describes a method of spectrophotoscopic analysis to analytically find the content of sugars in juice.
In this case too there is no reference to a classification of the basic food product according to the calorimetric analysis.
The document WO-A-95/21242 describes a method to determine the colors of beer, and its level of bitterness, by illuminating the beer with a light of a particular wavelength, causing its iso-xcex1-acids to fluoresce, monitoring the level of fluorescence and comparing it with known reference parameters.
This document does not teach a method to classify a food product made of juice either.
Moreover, none of the known solutions provides to integrate the color data with existing instruments, for example with those which monitor the sugar level of the juice.
The present Applicant has devised and embodied this invention to overcome these shortcomings in an economical, functional and extremely practical manner.
The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the idea of the main embodiment.
The purpose of the invention is to achieve a method, and relative device, suitable to perform an objective evaluation of the quality of a grape juice so as to allow the selective discrimination of a plurality of quality levels relating to the basic product from which the juice is obtained according to the actual composition characteristics of the said juice.
A further purpose is to achieve a device suitable to perform this quality evaluation which is economical, practical and compatible with existing equipment.
According to the invention, the method to evaluate the quality of juices, obtained from grapes, provides to evaluate the presence and percentage of coloring substances in the juice by means of emitting an optical signal which passes through the sample of juice and then to monitor a significant calorimetric parameter.
To be more exact, the invention provides to emit a beam of light directed towards the sample of juice to be analysed, to receive the optical signal transmitted through this sample, and to process the optical signal received to acquire information relating to the presence and percentage of coloring substances.
According to the presence and percentage of these coloring substances, the invention provides to construct an analytical classification of the basic fruit or vegetable product to sub-divide said grapes, into a plurality of quality classes.
In a preferential embodiment, the device which achieves the method according to the invention comprises:
a source of light associated with a fiber-optic transmission mean, or guide, suitable to convey the beam of light through the sample of juice to be analysed,
a reception element consisting of a fiber-optic spectrometer suitable to measure the transmittance or absorbance of the juice to be analysed, and
a processing unit, equipped with specific software, suitable to receive the information relating to the optical parameters taken from the reception element and to supply the estimation of the content of coloring substances in the juice, from which the phenol quality of the basic fruit or vegetable product can be found.
The use of a fiber-optic source is not absolutely necessary to achieve the invention, but it is preferential, since it guarantees that the analysis is immediate and therefore the results are too.
In one embodiment of the invention, the source of light consists of a tungsten lamp and the fiber-optic spectrometer is suitable to discriminate light signals at least in the range of frequencies between 190 nm and 850 nm, that is, substantially in the field of the visible and the ultraviolet.
According to the signal received and its position in the spectrum of frequencies discriminated by the fiber-optic spectrometer, the processing unit is able to quantify the content of coloring substances (for example the anthocyanins, or the red and/or yellow polymers) contained in the grape juice, and consequently is able to classify the basic product, for example the grapes, into a defined quality and commodity level.
By means of this evaluation criterion, which can integrate or replace the procedures of sugar or acid classification which are already used, it is possible to discriminate grapes or other fruit and vegetable products more rigorously and selectively than happens in the state of the art. It is therefore possible to devise a scale comprising a plurality of quality levels inside which the various products from which the juices analysed are obtained can be placed according to their content in terms of coloring substances.
In a preferential embodiment, the device which achieves the calorimetric evaluation of the grapes is integrated into the existing equipment suitable to carry out the analysis of the sugar content of the juice.